Latest About Guitar Amps Newsletter
Welcome to the latest update from About-Guitar-Amps.com. I hope you find the information here useful.
On a personal note - Please see the P.S at the end of the Newsletter
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About-Guitar-Amps Newsletter
As always, please contact us if you have suggestions related to Guitar Amps that you would like to see on the website or in
our newsletters, or in fact if you would like to write an article for the newsletter : ) You can email or use the contact form on
the website.
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New Schematics Added since the last Newsletter Latest Guitar Amp Schematics
Hope these help : )
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Overdrive your amplifier at your peril !How not to damage your speakers !
There's a lot talked about overdriving amps, and how this can damage your speakers. Some say the reason is that when an amp is
driven to the point it 'clips' - the squaring of the waveform
produces large amounts of odd harmonics which in turn achieve higher power outputs which damage speakers, particularly Mid and Hi Frequency
drivers. This is of course true, but this isn't the whole story.
I came across an excellent explanation of what happens the other day. By understanding this I hope it will help you to protect your
speaker systems in the future. The article was a bit techie so I've edited it to give you an overview...
When sine waves clip severely they resemble square waves in shape, introducing massive distortion.
1. First you need to know that in the extreme case, a perfect square wave contains a huge amount of harmonics and at the
highest level.
2. A slightly clipped sine wave contains the same frequencies but at lower levels which is why it's not a perfect sine wave or
square wave.
3. A perfect sine wave only contains the one frequency (called the fundamental frequency)
To demonstrate how speakers/tweeters are blown we're going to feed a sine wave into a 100 watt amplifier and overdrive it.
This is then connected to a speaker cabinet rated at 200 watts, by the time it had made it through the cross-over to the tweeter, the power
would amount to only a couple of watts or so. So you can see that it isn't purely the fact that we're feeding the speaker with an
clipped signal. (The tweeter wouldn't be rated at 200 watts, but probably 10 to 20 watts or so, but even so we're not overdriving it are we)
Ok - so why is it that a 100 watt amp driving a 200 watt cab could blow tweeters (Hi frequency drivers)?
What's actually happening is 'Compression' Let me explain....
Today’s newer higher quality amplifiers have greater dynamic range and sound better when clipped with musical transients than older
amplifier designs. So it is more likely that someone might overdrive and clip newer amplifiers on low frequency dynamic peaks
and not hear the distortion.
If you look at fig 3. below you'll see the result of monitoring the output from a 100 watt amplifier which is being
overdriven. You will see that in the graph the low frequency component is clipping and limited to 100 watts. The high frequency component
isn't clipping and is about 10 watts or so.
OK - lets overdrive the amp even more. Look at fig 4. below and you'll see that the low frequency component is
clipping even more but still limited to 100 watts. The high frequency component is still rising in power though, in fact
it's much higher than in the previous graph, and if we overdrive the amplifier even more, the high frequency component will carry on
rising until it reaches nearly 100 watts. This is in the region of 5 or 10 times the power the tweeter was designed to handle in our
example, and of course it will fail long before maximum output from the amplifier is acheived.
So now you can see how easily it is for someone who isn't careful to damage speakers and tweeters. I know many amps these days
have clip lights to warn of overdriving but in my experience many are very slow or late to react, so if you want to protect your
speakers always keep the input gain down to a reasonable level. You should never see the 'clip light' on... ever!
Connecting more than one speaker to your amplifier? Use the Free AGA Impedance
Calculator.
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Anyone out there interested in Schematics on CD or DVD?
Finding schematics online is great. You may remember when you used to have to phone the manufacturer and either pay a fortune for a
hard copy or be told to go away 'cause you don't have an account with them - or maybe you're not that old :)
Well how about all the Schematics we have online on a DVD. Wouldn't that be even easier?
Wouldn't you pay $8.00 (£4.00) plus postage to make life just that bit more convenient for you?
If you would, then let me know.
Use http://www.about-guitar-amps.com/Contact_Us.html to let me
know/order and I'll get back to you with the total cost including postage.
Please include your full address and email.
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Your Feedback Welcome here http://www.about-guitar-amps.com/Contact_Us.html
More stuff next month on Amps, Speakers and all things bright and beautiful
See you next time : )
David
PS - Our band (Comfort Zone) have recorded a Charity CD Single which is available as a download or CD. It's a
great song and 100% of the profits goes towards buying a breathing machine for children in our local hospital. It's a much needed
machine. Please help.
Go to http://www.comfortzonetheband.com Thanks very much : )
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